Almost all PVC that is used in extruded profiles (windows, siding, and doors) is impact-modified to some extent. Recently there has been an increased interest in composition of wood and PVC, particularly for use in home siding applications. Such composites are highly desirable because they resemble traditional wood siding. Moreover, such composition raises the sag temperature of PVC and thus permits the use of dark colors in the composite siding. See, e.g., U.S. Pat. Nos. 6,011,091, 6,103,791, and 6,066,680, and US Patent Application 2003/0229160.
To broaden markets and opportunities for PVC, various reinforcing fillers such as fiberglass or minerals are compounded into rigid PVC formulations in order to increase the stiffness (flexural modulus) of the polymer. Unfortunately, other physical properties are degraded by the addition of the reinforcing filler, usually in direct proportion to the amount of such filler that is added. Consequently, end users of the rigid PVC formulations are constantly searching for additives that prevent or minimize the reduction of such desirable properties. It is also desirable to prevent or minimize the loss of impact properties of the PVC, to improve or reduce the molten viscosity, or to minimize the loss in stiffness of PVC (as compared to the unmodified PVC).